The First Regiment, Texas Mounted Riflemen, was the first regiment in Texas to be mustered into Confederate service in 1861. On March 4, 1861, Confederate secretary of war Leroy Pope Walker directed Benjamin McCulloch to raise a regiment of ten companies of mounted riflemen to protect the Texas frontier between the Red River and the Rio Grande. McCulloch, hoping for a command east of the Mississippi River, turned the colonel's commission over to his brother, Henry Eustace McCulloch, who, on February 5, 1861, had been appointed to the rank of colonel by the state Committee of Public Safety and already had five under-strength companies along the state's northwestern frontier to replace the United States troops withdrawn after secession.
In mid-March Henry McCulloch arrived in Austin, where he recruited men for five additional companies for the new regiment. By the early part of April he had his regiment organized with men recruited from Bexar, Travis, Gonzales, Bell, Comanche, Bosque, Rusk, Burleson, and Lamar counties. The men already on the frontier who wished to join the new regiment had to be mustered out of state service and into Confederate service. By mid-April McCulloch's new regiment entered Confederate service as the First Regiment, Texas Mounted Riflemen, also known as the First Texas Mounted Rifles. This was not only the first regiment in the state organized for Confederate service, but the original commission to Ben McCulloch was one of the first in the Confederacy.
At San Antonio Henry McCulloch was elected colonel, Thomas C. Frost lieutenant colonel, and Edward Burleson, Jr., major. By the following month the ten companies of the regiment occupied a line of forts from Camp Jackson, at the confluence of the Red River and the Big Wichita, southwestward to Fort Belknap, Camp Cooper, Fort Phantom Hill, Fort Chadbourne, Camp Colorado, Camp Concho (at present-day San Angelo), Fort McKavett, and Fort Mason.
McCulloch's patrols covered the regiment's 400-mile line, to which were added regular expeditions of two to three weeks into suspected haunts of hostile Indians northwest of the line of forts. The summer and fall of 1861 saw diminished Indian activity compared to the years before the war, and no major incursions of Indians into the settlements. McCulloch returned to San Antonio in September to take temporary command of the Department of Texas, and in December he accepted command of the Western Military District of Texas. As his attention turned to defense of the Texas coast his regiment on the Indian frontier was commanded for a time by his adjutant and senior officers.
The enlistment for the regiment was to run out in the spring of 1862; rumors spread that Confederate officials planned to remove it from the frontier. The regiment mustered out in mid-April 1862 at Fort Mason, and the state-financed Frontier Regiment replaced it on the frontier. Some of the men returned to frontier service, but most enlisted in the Eighth Texas Cavalry Battalion, which later became part of the First Texas Cavalry Regiment.